A recently advancing tendency for reducing unhealthy products in the engine exhaust gases resides in retarding the ignition timing or power timing, so called of the engine, so as to reduce the quantities of NO.sub.x ; HC; CO and the like. The most generally adopted means for retarding the engine power timing resides in means adapted for operational control of vacuum advancer operatively connected with the conventional distributer and under the utilization of the negative pressure prevailing in the engine intake manifold.
The operational mode of the above kind of control mechanism is such that when the accelerator pedal is depressed under the idling conditions of the engine a kind of vacuum-operated retardational operation is employed for retarding the execution of timing advancing operation of the engine, so as to improve the exhaust gas quality. For this purpose, the vacuum fluid passage quantity is subjected to proper reduction so as to retard the attainment of fully advanced angle position of the distributor.
On the contrary, when the engine revolutional speed is reduced, the ignition time adjuster senses automatically a negative pressure reduction in the engine intake manifold and it is utilized to allow full passage of the vacuum pressure gaseous fluid, so as to adjust the ignition timing of the engine in its retardation-recovering sense.
In the conventional ignition timing adjuster, as its representative structural mode, a valve member made of sintered alloy and having an orifice opening is pressed into a housing of said adjuster, said housing having a passage opening for cooperation of said orifice and normally being closed by a resilient valve adapted for control of vacuum fluid for the necessary control of the ignition timing.
According to our study, it has been found that when the vacuum fluid pressure is led to act upon the resilient valve in its closing direction, optimum valve closure can be attained only with great difficulty.